James's story, which found its first readers as a piece of Twilight-inspired fan fiction, took just 11 weeks to pass the million marker – it has now sold 1,162,637 copies, according to book sales monitor Nielsen BookScan – and takes its place in the record books, ahead of The Da Vinci Code, which took 36 weeks to top one million.

Publisher Arrow is now on its 17th reprint in the UK, and digital sales are also booming, with Amazon.co.uk announcing earlier this week that James had become the first author to sell more than one million books in its ebook store.

"The trilogy is selling incredibly strongly in both ebook and printed formats – we have just reprinted the physical books for the 17th time and the latest figures show that this is truly a phenomenon," said Charlotte Bush, director of publicity and media relations at Cornerstone. "When we first bought the books, people asked if women would be willing to be seen reading the books in public. I've always believed they would. Our job was to ensure they were the books everyone was talking about. What is so exciting is to see the evidence – women, and men too – are reading them on buses, in parks, on the beach, in nail bars, in restaurants – I even saw one woman walking down the street with her nose in the book!"

Bush said the publisher had even received an email from a satisfied customer who wanted to pass on a message to James: that as a result of reading the first book, she was now seven weeks pregnant.

But the overall adult weekly sales record still belongs to Brown, whose most recent novel The Lost Symbol sold over 500,000 copies in a week in 2009, and Rowling's last three Harry Potter hardbacks still hold the overall weekly record, selling 1.8m, 1.4m and 1.4m copies, according to The Bookseller.